The function of the proposed research project is to assess physiological, subjective and cognitive factors associated with muscle-contraction headache and to investigate the practicality of viewing muscle-contraction headache as a psychophysiological disorder according to a proposed hypothetical model. The proposed project consists of three studies evaluating physiological and subjective events during rest, stress and post-stress conditions; during headache and nonheadache states; and between subjects with frequent and those with infrequent muscle-contraction headaches. In the first study, 24 subjects with frequent and 24 subjects with infrequent muscle-contraction headaches will be exposed to several conditions (rest, two types of stressors, recovery from stress) while physiological (EMG from three sites, skin conductance, heart rate) and subjective responses (measures of subjective discomfort during stressors) are measured. In the second study, 25 subjects with frequent muscle-contraction headaches will be exposed to conditions similar to Study 1 but during headache and nonheadache states. In counter-balanced order, subjects will enter the psychophysiology laboratory during headache and nonheadache states and undergo rest, stress and stress-recovery conditions while physiological and subjective responses are monitored as in Study 1. In the third study, 24 subjects with frequent and 24 subjects with infrequent muscle-contraction headaches will be exposed to prolonged (1-2 hours) stress (cognitive activity/arithmetic problems) while physiological and subjective responses (identical to the previous studies) are monitored. The proposed series of studies is designed to provide a better understanding of the physiological and subjective factors associated with muscle-contraction headache.